1. Field of the Invention
The present invention pertains to an apparatus and method of providing high frequency variable pressures to an airway of a patient, and, in particular, to an apparatus and method of providing high frequency variable pressures in which a valve generates the pressure oscillations in the delivery of gas to or from the patient independent of patient effort.
2. Description of the Related Art
Many people have difficulty clearing secretions, such as mucous or fluids, from their respiratory system. In a healthy patient, accumulated secretions are removed from the respiratory system by clearing the throat or coughing. Some patients, however, such as those with a weakened respiratory system, may not be physically able to perform such a secretion clearing movement with sufficient strength to remove or loosen the secretion.
To address this problem, a device is known that creates an abrupt pressure variation in the patient's airway, particularly during exhalation, to assist in dislodging or removing the secretions. An example of such a device is a hand-held flutter valve, which uses a ball valve to create the pressure oscillations. When the patient breathes into the flutter valve, the force of the patient's exhalation moves a ball off a valve seat to open the valve. Gravity immediately urges the ball valve back onto the seat to obstruct the patient's expiratory flow until the expiratory force is sufficient to again urge the ball off of the seat. This process repeats as the patient exhales until the patient's expiratory force is not great enough to move the ball off of the seat. A series of pressure spikes occur in the patient's airway as a result of the temporary flow interruption caused by the closing and opening of the ball valve to facilitate loosening and removal of the patient's airway secretions.
There are disadvantages associated with this flutter valve secretion clearance device. For example, proper seating of the ball on the valve seat is only possible if the device is held in its upright position. Therefore, the conventional flutter valve device is very position sensitive. In addition, because the patient's own expiratory force is used to move the ball to the open position, the flutter valve cannot be used by patients with very weak respiratory systems who have very low expiratory flow rate.
Another device that provides pressure oscillations to the patient's airway is the Emerson Cough-a-Lator, produced by Emerson, Inc. This device provides both a positive and a negative pressure to the patient's airway to assist in secretion clearance. A mechanism in the device physically moves a portion of a patient circuit in a windshield wiper fashion between a first position, where a positive pressure output from a blower is coupled to the patient, and a second position, where a negative pressure at the input of the blower is coupled to the patient. This device is relatively large, complex, bulky and expensive, and, therefore, is not readily portable. It is also generally not convenient or easy to set up and use.